Immunoassays are ligand binding assays where the specific recognition of an antibody to the specific binding site of an analyte is exploited. The immunoassays usually involve the immobilisation of a ligand (antibody, other protein, hapten etc.) to a solid phase (support material) that will, in turn, be recognised by the analyte to be determined. The use of specific labelled detecting agents allows the subsequent detection and quantitation of the analyte in an aqueous sample. The amount of analyte present in the sample is a function of the bound labelled detecting agent: inversely proportional in competitive assays and directly proportional in noncompetitive assays.
Different immunoassays have been reported in which the solid phase that contains the ligands are plastic tubes (U.S. Pat. No. 3,646,346), discs (J. Lab. and Clin. Med., 70: 820, 1967), porous supports (U.S. Pat. No. 4,708,932, U.S. Pat. No. 4,459,360) and beads (Clin Chem. 37: 1521, 1991). The quantitation of analyte in these systems is carried out by the construction of individual external calibration curves; the concentration of each analyte being in a separate solid phase unit. These calibration curves may be stored and used to control runs of samples in which a particular analyte has to be measured.
There is now a growing awareness of the advantages of carrying out multianalyte determination on microarray-based technologies. These systems present greater flexibility and versatility with high throughput and sensitivity. Multiple ligands can be disposed on the surface of the support, each one defining individual discrete test regions (DTRs) of defined small volumes (pl or nl), permitting the simultaneous multiplexed detection and quantitation of multiple analytes in one sample. The amount of sample required per assay is also greatly reduced.
GB-A-2324866 discloses suitable microarrays that may be used in an immunoassay.